Use this test to determine whether a traditional P chart or a Laney P' chart is more appropriate to chart the proportion of defectives in your sample. If the test determines that your data exhibit overdispersion or underdispersion a Laney P' chart may more accurately distinguish between common cause variation and special cause variation.

The records management staff at a small hospital improved the accuracy and completeness of patient records. To sustain these improvements, the staff tracks the number of incomplete and inaccurate records that are filed each day.

The average subgroup size is more than 2500. Because of the large number of records, the staff wants to determine whether to use a Laney P' chart.

Data: DefectiveRecords.MTW (available in the Sample Data folder).